diff --git a/extension/lib/wallet/checkable.ts b/extension/lib/wallet/checkable.ts
index 9a31e4e17..27ea9bf74 100644
--- a/extension/lib/wallet/checkable.ts
+++ b/extension/lib/wallet/checkable.ts
@@ -77,6 +77,15 @@ export namespace Checkable {
   }
 
 
+  function checkOptional(target, prop, path): any {
+    console.assert(prop.propertyKey);
+    prop.elementChecker(target,
+                        prop.elementProp,
+                        path.concat([prop.propertyKey]));
+    return target;
+  }
+
+
   function checkValue(target, prop, path): any {
     let type = prop.type;
     if (!type) {
@@ -84,7 +93,8 @@ export namespace Checkable {
     }
     let v = target;
     if (!v || typeof v !== "object") {
-      throw new SchemaError(`expected object for ${path}, got ${typeof v} instead`);
+      throw new SchemaError(
+        `expected object for ${path.join(".")}, got ${typeof v} instead`);
     }
     let props = type.prototype[chkSym].props;
     let remainingPropNames = new Set(Object.getOwnPropertyNames(v));
@@ -119,7 +129,7 @@ export namespace Checkable {
         propertyKey: "(root)",
         type: target,
         checker: checkValue
-      }, []);
+      }, ["(root)"]);
     };
     return target;
   }
@@ -164,6 +174,29 @@ export namespace Checkable {
   }
 
 
+  export function Optional(type) {
+    let stub = {};
+    type(stub, "(optional-element)");
+    let elementProp = mkChk(stub).props[0];
+    let elementChecker = elementProp.checker;
+    if (!elementChecker) {
+      throw Error("assertion failed");
+    }
+    function deco(target: Object, propertyKey: string | symbol): void {
+      let chk = mkChk(target);
+      chk.props.push({
+                       elementChecker,
+                       elementProp,
+                       propertyKey: propertyKey,
+                       checker: checkOptional,
+                       optional: true,
+                     });
+    }
+
+    return deco;
+  }
+
+
   export function Number(target: Object, propertyKey: string | symbol): void {
     let chk = mkChk(target);
     chk.props.push({propertyKey: propertyKey, checker: checkNumber});
diff --git a/extension/lib/wallet/wallet.ts b/extension/lib/wallet/wallet.ts
index 788d3f6c6..fe3148c9b 100644
--- a/extension/lib/wallet/wallet.ts
+++ b/extension/lib/wallet/wallet.ts
@@ -162,6 +162,9 @@ export class Contract {
   @Checkable.String
   fulfillment_url: string;
 
+  @Checkable.Optional(Checkable.String)
+  repurchase_correlation_id: string;
+
   static checked: (obj: any) => Contract;
 }
 
@@ -761,6 +764,7 @@ export class Wallet {
    * Withdraw one coins of the given denomination from the given reserve.
    */
   private withdraw(denom: Denomination, reserve: Reserve): Promise<void> {
+    console.log("creating pre coin at", new Date());
     let preCoin = createPreCoin(denom, reserve);
     return Query(this.db)
       .put("precoins", preCoin)
diff --git a/extension/lib/wallet/wxmessaging.js b/extension/lib/wallet/wxmessaging.js
index 6310d6cd4..4218d6aa1 100644
--- a/extension/lib/wallet/wxmessaging.js
+++ b/extension/lib/wallet/wxmessaging.js
@@ -61,7 +61,7 @@ System.register(["./wallet", "./db", "./http", "./checkable"], function(exports_
                 catch (e) {
                     if (e instanceof checkable_1.Checkable.SchemaError) {
                         console.error("schema error:", e.message);
-                        return Promise.resolve({ error: "invalid contract", hint: e.message });
+                        return Promise.resolve({ error: "invalid contract", hint: e.message, detail: detail });
                     }
                     else {
                         throw e;
@@ -80,12 +80,12 @@ System.register(["./wallet", "./db", "./http", "./checkable"], function(exports_
         );
         var _a;
     }
-    function dispatch(handlers, db, req, sendResponse) {
+    function dispatch(handlers, req, sendResponse) {
         if (req.type in handlers) {
             Promise
                 .resolve()
                 .then(function () {
-                var p = handlers[req.type](db, req.detail);
+                var p = handlers[req.type](req.detail);
                 return p.then(function (r) {
                     sendResponse(r);
                 });
@@ -125,7 +125,7 @@ System.register(["./wallet", "./db", "./http", "./checkable"], function(exports_
             var wallet = new wallet_1.Wallet(db, http, badge);
             var handlers = makeHandlers(db, wallet);
             chrome.runtime.onMessage.addListener(function (req, sender, sendResponse) {
-                return dispatch(handlers, db, req, sendResponse);
+                return dispatch(handlers, req, sendResponse);
             });
         })
             .catch(function (e) {
diff --git a/extension/lib/wallet/wxmessaging.ts b/extension/lib/wallet/wxmessaging.ts
index 34d9d469e..934984722 100644
--- a/extension/lib/wallet/wxmessaging.ts
+++ b/extension/lib/wallet/wxmessaging.ts
@@ -77,7 +77,7 @@ function makeHandlers(db: IDBDatabase,
       } catch (e) {
         if (e instanceof Checkable.SchemaError) {
           console.error("schema error:", e.message);
-          return Promise.resolve({error: "invalid contract", hint: e.message});
+          return Promise.resolve({error: "invalid contract", hint: e.message, detail: detail});
         } else {
           throw e;
         }
@@ -107,12 +107,12 @@ class ChromeBadge implements Badge {
 }
 
 
-function dispatch(handlers, db, req, sendResponse) {
+function dispatch(handlers, req, sendResponse) {
   if (req.type in handlers) {
     Promise
       .resolve()
       .then(() => {
-        const p = handlers[req.type](db, req.detail);
+        const p = handlers[req.type](req.detail);
 
         return p.then((r) => {
           sendResponse(r);
@@ -155,7 +155,7 @@ export function wxMain() {
            let wallet = new Wallet(db, http, badge);
            let handlers = makeHandlers(db, wallet);
            chrome.runtime.onMessage.addListener((req, sender, sendResponse) => {
-             return dispatch(handlers, db, req, sendResponse)
+             return dispatch(handlers, req, sendResponse)
            });
          })
          .catch((e) => {
diff --git a/extension/pages/confirm-contract.html b/extension/pages/confirm-contract.html
index d2245a9fb..ca524a61a 100644
--- a/extension/pages/confirm-contract.html
+++ b/extension/pages/confirm-contract.html
@@ -21,7 +21,7 @@
     </aside>
 
     <section id="main">
-      <article id="contract"></article>
+      <article id="contract" class="fade"></article>
     </section>
 
   </body>